1. Field
The present invention relates generally to communication, and more specifically to techniques for detecting discontinuous transmission (DTX) frames in wireless communication systems.
2. Background
Wireless communication systems are widely deployed to provide various types of communication. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, and frequency division multiple access (FDMA) systems. A CDMA system may be designed to implement one or more standards such as IS-2000, W-CDMA, IS-856, IS-95, and so on.
Many newer generation wireless communication systems, such as IS-2000 and W-CDMA systems, support flexible operation. For example, data may be transmitted at any one of a number of supported rates on the forward and reverse channels. Moreover, a forward channel may be operated in a non-continuous manner whereby data frames may not be transmitted some or most of the time. This non-continuous transmission is also referred to as discontinuous transmission (DTX). For IS-2000 and W-CDMA systems, no data frames are actually transmitted on the forward channel during periods of no transmission, and these non-transmitted frames are often referred to as DTX frames.
For certain functions, it is necessary to accurately detect what type of frame was received in each frame interval. For example, in an IS-2000 system, a base station is allowed to discontinue its transmission on a Forward Dedicated Control Channel (F-DCCH) when it has no data to send to a terminal (e.g., a cellular phone). The F-DCCH may be configured to carry a Forward Power Control Subchannel, which includes power control (PC) bits for the terminal. The PC bits are transmitted on the F-DCCH even during periods of no data transmission. If the Forward Power Control Subchannel is carried on the F-DCCH, then the terminal would need to determine whether a good, bad (erased), or DTX frame was received in each frame interval. This information is needed to properly control the transmit power of the F-DCCH, so that the PC bits for the Forward Power Control Subchannel can be correctly detected by the terminal even during periods of no data transmission.
The determination of whether or not a received frame is a good frame is typically trivial, and may be made based on a cyclic redundancy check (CRC) value included in each transmitted data frame. However, the determination of whether the received frame is erased or DTX (if the CRC fails) is more challenging. This is because a failed CRC can result from a data frame being transmitted but received in error (i.e., an erased frame), or no data frame being transmitted (i.e., a DTX frame). Some other metrics besides the CRC would then be needed to detect for DTX frames.
There is therefore a need in the art for techniques to accurately detect DTX frames on a forward channel in wireless (e.g., IS-2000 and W-CDMA) communication systems.